Automatic leveling mechanism for hoisting trucks



Sept. 29, 1953 A. s. HAMILTON, JR

AUTOMATIC LEVELING MECHANISM FOR HOISTING TRUCKS 4 Sheets-Sheet 1 Filed 001'.- 23, 1951 E 2 mm 6 2 E m 3 m R a M A m a HM 2 J N m U AFUB W7 HOA am 4n L s 2 4 WM 8 0 U N PR 8 A D 6 m H 5/ NIL J 4 a a 5 Sept. 29, 1953 A. s. HAMILTON, JR 2,653,679

AUTOMATIC LEVELING MECHANISM FOR HOISTING TRUCKS Filed Oct. 25, 1951 4 Sheet s-Sheec 2 7' OP 0F $740K OF PAPER Sept. 29, 1953 AUTOMATIC LEVELING MECHANISM FOR I-IOISTING TRUCKS Filed Oct. 23

. [p o o o o o o o o o A. S. HAMILTON, JR

O I o 1 n 'c, A; 5%} d 4 Sheets-Sheet 3 I I I I 1 I I I INVENTOR. AFYHUF 5 WILTUIXJ/Q ATTORJVEY.

Sept. 29, 1953 A. s. HAMILTON, JR

AUTOMATIC LEVELING MECHANISM FOR HOISTING TRUCKS Filed 061;. 25, 1951 4 Sheets-Sheet 4 IN V EN TOR. APT/1M? 5. ML 727 M ATTORNEY.

Patented Sept. 29, 1953 UNITED STATES PATENT OFFICE AUTOMATIC LEVELING MECHANISM FOR HOISTIN G TRUCKS Arthur S. Hamilton, Jr., Brighton, N. Y.

Application October 23, 1951, Serial No. 252,753

12 Claims. 1

This invention relates to a hoisting truck of the type provided with a load support or table that can be raised or lowered to position a load at any level within the limits of the truck, and has for its purpose to afford means for automatically raising or lowering the support, stopping such movement when the load shall have reached a predetermined level and automatically resuming the movement when the load shall have been reduced or increased in height respectively, depending on whether the load is being raised or lowered.

A further purpose of the invention is to aiford mechanism for automatically raising a load support of a truck intermittently through uniform distances so that lifts or sheets of material com prising the load can be removed from the top and the support automatically raised to bring successive portions of the load to the predetermined level for convenient removal of lifts or sheets onto a cutter table or the like onto which the sheets are to be placed.

An additional object of the invention is to provide a truck with electrical mechanism which automatically raises or lowers sheets or lifts of material through predetermined distances successively, governing the operation of the automatic mechanism by the position of the topmost portion of the load in relation to the predetermined level as determined by a beam of light and photocell onto which the beam is reflected.

A more specific purpose of the invention is to accomplish the desired objectives by the provision of a vertically adjustable photocell that is operatively associated with electrical control mechanism which functions automatically to stop movement of the load upwardly when a beam of light striking the elevating load is reflected onto the photocell, and to stop movement of the load downwardly when the load moves beneath the path of the beam of light which is then no longer intercepted and therefore not reflected onto the photocell.

Thus the load support or table can be elevated to the desired level to permit removal of sheets or lifts onto a cutter table by sliding them off from the stack onto the cutter table, and after a lift or number of sheets are removed, the load is automatically elevated until the top of the load is at the original level and intercepts the beam of light, stopping further movement, this operation being repeated as each lift or series of sheets are removed from the top of the load, and on lowering', the reverse operation takes place since the light beam striking the load is reflected onto the photocell and causes the load support to move downwardly until the top of the load is beneath the light beam, stopping further movement until an additional lift or additional sheets are added to the top of the load, again intercepting the light beam and reflecting it, to repeat the cycle.

Still another object of the invention is to provide automatic electrical raising and lowering mechanism with controlling devices that enabl a load to be raised or lowered by manual control, or to be raised or lowered automatically by means that effects intermittent movements of the load support upwardly or downwardly, stopping it whenever the load reaches a predetermind position and its upper portion is in the path of or positioned beneath a light beam respectively, thus moving the support upwardly or downwardly aumatically in preadjusted increments.

An additional purpose of the invention is to afford efiicient and practical control mechanism including a vertically adjustable housing containing lamp mechanism including a lamp, reflector, and condensing lens operable to project a beam of light toward the load and a condensing lens which receives the beam of light when the latter is reflected from the load and directs it onto a photocell in the housing for operating the control mechanism.

A further object of the invention is to afford electrical mechanism for either manually controlling movement of the load support or table upwardly or downwardly through any distance, or permitting such electrical mechanism to be governed through an arrangement of electrical circuits such that a photocell functions to operate the electrical mechanism and move the load support upwardly or downwardly automatically through successive predetermined distances, dependent upon the vertical positioning of the photocell.

To these and other ends, the invention consists in the construction and arrangement of parts that will appear clearly from the following description when read in conjunction with the accompanying drawings, the novel features being pointed out in the claims following the specificaion.

In the drawings:

Fig. 1 is a view in side elevation illustrating a truck constructed in accordance with a preferred embodiment of the invention;

Fig. 2 is a rear elevation of the same;

Fig. 3 is an enlarged elevation showing the mechanism appearing at the upper part of Fig. 2, with the front of the housing of the electrical cgntrol means removed to show the interior there- 0 i Fig. 4 is a view in side elevation of the parts appearing at the upper portion of Fig. 3;

Fig. 5 is a view in rear elevation of the vertically adjustable lamp mechanism and photocell;

Fig. 6 is a vertical sectional view through the lamp housing;

Fig. 7 is a vertical sectional View showing the photocell and vertically adjusting means for the lamp mechanism and photocell;

Fig. 8 is a horizontal sectional view on line 88 of Fig. 7;

Fig. 9 is an enlarged detail perspective view of the adjustable locking device which holds the lamp mechanism and photocell in their vertically adjusted positions;

Fig. 10 is a diagrammatic view showing the light beam projecting means in relation to the reflecting load and photocell, and

Fig. 11 is a diagrammatic View of the circuits leading to the hoist motor and electrical control means which ar governed either by hand, or automatically by the photocell, the photoelectric relay control switch and automatic selector switch being shown in position for automatic raising, and the main switch and hand selector switch being shown in on positions.

Referring more particularly to the drawings in which like reference numerals throughout the several views indicate the same parts and to Figs. 1 to 3 inclusive, 1 designates the base of a truck provided with the usual floor-engaging wheels 2 and 3, handle 4 for moving the truck over a floor, and uprights 5 upon which is mounted. for vertical travel the load support or table 6 comprising a fork that is suitably guided on the uprights 5 and carries a sprocket rotatably mounted thereon and engaged by the operating chain 8 which travels around said sprocket I and has one end connected to the motor housing at 9. The motor housing is shown as suspended from the top of the truck by a hook H, while the portion of the chain 8 adjacent to the connection 9 extends downwardly and thence upwardly in a loop, see Fig. 2, thence around a sprocket wheel l2 that is connected to and driven by the hoist motor l3, and thence downwardly and around sprocket wheel 7 carried by the load support 6. and after leaving sprocket l the chain 53 extend: upwardly and is connected to hook H! which is suspended from the cross-member It: at the top of the uprights 5, and from which the previously mentioned hook H is also supported. Instead of suspending the hoist motor and chain by the hooks H and 14, they may if preferred be permanentl and rigidly attached to the top of the frame.

The structure thus far described is part of a conventional and known hoisting mechanism and forms no part of the present invention, which has to do with the electrical control means to hoist motor l3 for controlling the same either manually or automatically, and which will now be described in detail.

In the conventional operation of hoist motor it, which is controlled by a reversing drum switch It, see Figs. 4 and 11, the switch is operated manually through a rock arm ll which is pivoted at E8 on a stationary bracket and in turn connected by link 19 to the reversing switch arm, so that the load support or fork 6 is moved upwardly or downwardly by operating the rock arm il in one direction or the other manually, and the present invention has to do with electrical means for operating said rock arm H to control the hoist motor, such electrical means being so constructed and arranged that the load support can be moved automatically upwardly or downwardly through successive increments of distance whereby the height of the load automatically controls movement of the hoist motor by stopping the motor when the load moves upwardly a predetermined distance and automatically starting the motor again when a lift or sheets have been removed from the pile, or reversely, stopping the hoist motor when the load moves downwardl a predetermined distance following which the hoist motor is automatically started when the height of the load is increased as by piling a lift or additional sheets thereon, or the load can be raised or lowered by manual control when desired.

These results are accomplished through a photocell that is in the path of a reflected beam of light which strikes the top portion of the load on the support or fork and is reflected back onto the photocell when the load is at such elevation that its top portion is in the path of the beam of light, and under this position of the load, the hoist motor is automatically stopped if the load is moving upwardly and automatically started if the load is moving downwardly. Thus when the load is traveling upwardly and reaches a point where it intercepts the beam of light, the hoist motor is automatically stopped and remains stopped until a lift or sheets have been removed from the top of the load sufficiently so that the beam or light is no longer reflected onto the photocell, whereupon the hoist motor is automatically started and the load travels upwardly through the predetermined distance. The reverse operation takes place when the load is traveling downwardly, the hoist motor operating to move the load downwardly while the load is in the path of the beam of light, and when the load has moved downwardly far enough so as no longer to lie in the path of the beam of light and reflect it onto the photocell, the motor is automatically stopped and remains stopped until a lift or sheets have been added to the load sufficiently to intercept the beam of light, whereupon operation of the hoist motor is resumed to continue dowwnard movement of the load support or fork.

In order to effect such movements, the rock arm I? which controls the reversing switch to the hoist motor has operatively connected thereto solenoids 2! and 22 respectively, see Figs. 4 and 11, which when actuated move the rock arm 51 from neutral or off position in a direction to operate the hoist motor tomove the load support upwardl or downwardly as the case may be. Solenoids 2i and 22 are controlled by suitable switches whereby they may be actuated automatically to move the load upwardly or downwardly in accordance with the position of the load with respect to a vertically adjustable beam of light which effects operation of a photoelectric relay in the manner that will now be described in detail.

Solenoids 2i and 22 are governed from switches 23, 2d and 25 respectively, the main or central switch indicated at 241 being adjustable to determine whether the operation of the hoist motor is to be automatic or manual. Switch 2% is shown in Figs. 3 and 11 in the off position, and when turned to the left or anti-clockwise from the vertical position shown in Fig. 3, the operation is hand controlled upwardly or downwardly. When main switch 2d is turned to the right or in a clockwisedirection, the operation of the hoist motor is automatic upwardly or downwardly. When switch 24 is in the automatic position, and

switch 25 is turned to the right or clockwise, the hoist motor is automatically operated to lower the fork or load support as long as the light beam is intercepted and to stop movement of the motor when the light beam is beneath and no longer reflected by the load, the hoist motor being again started when a lift or sheets have been placed on the load and intercept the light beam. When switch 25 is turned to the left or anti-clockwise, the hoist motor is automatically operated to elevate the fork or load support as long as the light beam is unintercepted by the top of the load and to stop movement of the hoist motor when the load has moved up high enough to intercept the light beam and reflect it onto the photocell, which then functions to stop the hoist motor until a lift or sufiicient sheets of the load have been removed from the top of the pile so as not to intercept the light beam, whereupon the photocell functions to start the motor again, thus moving the load upwardly in predetermined increments depending upon the adjusted elevation of the photocell.

In order to accomplish this, there is provided a housing 26, see Fig. 2, that is adjustable vertically on a post 21 mounted on a fixed supporting frame 28 and secured at its upper end as at 29 to the housing 3| containing the solenoids 2| and 22 and switch mechanism, which housing is mounted on the motor supporting frame and suitably tied to a vertical part of the truck frame. The housing 26 is provided with a lamp 32, reflector 33, and condenser lens 34, while 35 designates a condenser lens through which the light beam is reflected back from the top of the load onto the photocell 36 through a shield 31. The lamp mechanism and photocell unit are mounted on bracket 38, see Figs. 5 and '7, which carries a sleeve 39 that is slidable vertically on the vertical post 21, and 4| designates a handle connected to the sleeve 39 for adjusting the lamp mechanism and photocell vertically. These parts are held in their vertically adjusted position by a locking lever 42 that is pivoted to the sleeve 39 at 43 and held normally in looking position by a coil spring 44 connected to a pin 45 on the sleeve 39 and to the adjacent end of the locking lever 42, which has an opening 46, see Fig. 9, that embraces the vertical post 21. Looking lever 42 carries a dog 4'! that frictionally engages the adjacent surface of post 21 and holds the lamp mechanism and photocell in their position of vertical adjustment. The locking lever 42 is further provided with an opening 48 that embraces a pin 49 on the handle 4| and is movable downwardly against the action of spring 5| to release the lever from engagement with the post 21 and permit vertical adjustment of the lamp mechanism and photocell when desired to change the elevation at which movement of the load is to be stopped.

The photocell and light mechanism are thus adjustable vertically to any point on the post 21 to determine the point at which the hoist motor is stopped automatically during upward or downward travel of the load, depending upon the direction in which it is desired to move the load support. Assuming that the load support is traveling upwardly, with the light mechanism and photocell at a given adjusted position, when the load reaches a point high enough to intercept the beam of light and reflect it back onto the photocell, the latter functions to stop the hoist motor. The load support then remains station ary until a lift or sufficient number of sheets have been removed from the top of the load so as to 6 no longer intercept the light beam, and when this happens, the light no longer being reflected onto the photocell, the latter, through the photo-electric relay and electrical mechanism to be described presently, operates the hoist motor which again raises the load support through the predetermined distance. This automatic cycle con tinues as long as switch 24 is set to automatic position and switch 25 is set to raise position, see Figs. 3 and 11, and when switch 25 is set to lower position with switch 24 remaining in the automatic position, the load support is automatically lowered through predetermined distances successively, being stopped each time the load is below the beam of light and automatically started when sheets have been placed on the top of the load sufficiently to intercept the beam of light.

In Fig. 11 is illustrated the circuit arrangement for governing the solenoids 2| and 22, either automatically or manually, as follows: The hoist motor I3 is connected to conductors 52 and 53 of the current supply line through suitable conductors 54 and 55 respectively, leading from conductors 52 and 53 to the reversing drum switch l6 already referred to, while 55 and 51 designate conductors leading from opposite sides of the line to the aforementioned main or central switch 24, which is of the double-throw type, see Figs. 3 and 11. When switch 24 is in the off position, as shown in 11, the hoist motor is idle and when switch 24 is turned to the right or clockwise, it completes the circuit through conductors 5B and 59 to automatic transformer 55!, lamp 32, conductor 62 and contact '12. At the same time the circuit is completed through conductors 69 and H to the photoelectric relay 65, which when the photocell 36 receives the reflected beam, moves control switch 6:; downwardly, the latter being held normally in its uppermost position, see Fig. 11, by a spring not shown, while photocell 35 is connected to the photoelectric relay 65 by means of conductors 6'! and E3. The photoelectric relay is of conventional type and connected by conductors 69 and 7| to opposite sides of the line. The selector automatic switch 25, see Figs. 3 and 11, causes the load support to move upwardly or downwardly, depending upon its position, for automatic control of the hoist motor, and switch 23 permits moving the load support upwardly or downwardly, depending upon its position, for manual control of the hoist motor.

Fig. 11 show the position of the parts when the main or central switch 24 is in off position, selector hand switch 23 in off position, and selector automatic switch 25 is turned to position to effect automatic raising of the load support when switch 24 is moved to the automatic position. In the position shown in Fig. 11, the photoelectric relay'fiS is held in elevated position as already described, and switch 66 is elevated to the position indicated. When switch 24 is moved to the automatic or down position of Fig. 11, the circuit is closed through conductor 56, contact 72, and conductor 62 to the lamp mechanism, thence through conductor 58 and contact point 13 to switch 24 and to the other side of the line through conductor 5?, also through conductor 62 to switch 25, contact point l4, switch 65, contact point 15, and conductor '56 to solenoid 2| which effects raising of the load support automatically until the light beam is intercepted by the top of the load and the beam reflected onto the photocell 36, causing the photoelectric relay 65 to move the switch 66 downwardly. This breaks the circuit to the hoist motor and stops elevating of the load support until a lift or a suflicient number of sheet have been removed so that the light beam is no longer intercepted by the top of the load, whereupon the photoelectric relay 65 is released and elevated by its spring to the position shown in Fig. 11, and the load support again elevated and the cycle repeated.

If it is desired to lower the forl: or load support automatically, with switch 2% still in the automatic or down position referred to above, switch 25 is moved into engagement with contact H, see Fig. 11, and assuming that the top of a load is in the path of the light beam, the photocell causes photoelectric relay 55 to move the switch 66 downwardly into engagement with contact 18, the circuit thus being completed through conductor 79 to sol noid 22 which operates to lower the load support until the top of the load has moved out of the path of the light beam which is then no longer reflected onto the photocell. This releases the photoelectric relay 65, permitting switch 55 to move upwardly to the position shown in Fig. ll, and breaking the circuit, thus stopping the hoist motor which remains idle until a suificient number of sheets have been placed on top of the load to again intercept the light beam, which thereupon strikes the photocell, causing the photoelectric relay to be actuated and moving switch 5'5 again downwardly, operating solenoid 22 to eiiect further movement of the hoist motor downwardly, and the cycle just described is repeated.

When switch 2 l is moved to the hand position, referring to Figs. 3 and 11, for operation of the hoist motor by manual control, the circuit from conductor 56 through switch contact 8i and conductor 82 to the switch 23, which is movable upwardly into engagement with contact 83 for raising the load support and the circuit then completed through solenoid 2! to conductor and the other side of the line, or downwardly into engagement with contact 8& to complete the circuit through solenoid 22 to lower the load support, and thence to conductor 53 or the other side of the line.

In this manner, the worl: or load support is movable automatically when switch 2 is set to the automatic position, switch 25 being turned to the right, referring to Fig. 3, for lowering the load support automatically, or to the left for elevating the load support automatically. When switch 24 is set to the hand or manual position, the load support is moved upwardly or downwardly by operating switch 23 to raise or lower positions respectively. The exact position at which the load support stops its travel in either upward or downward movement during automatic control depends on the vertically adjusted position of the lamp mechanism, which may be adjustable in any desired manner.

While the invention has been described with reference to the particular structure herein shown, it is not limited to the details illustrated, and this application is intended to cover such modifications or departures as may come within the purposes of the improvement and the scope of the following claims.

Iclaim:

1. A lift truck including a load. support and a hoist motor connected thereto for raising or lowering the same, control mechanism operatively connected to the hoist motor, a photocell operatively connected to said control mechanism and arranged to receive a beam of light reflected from a load on the load support, and lamp mechanism arranged and'operating to project a beam of light toward a load on the support, said projected beam of light and said reflected beam being arranged at an acute angle to each other and the photocell and lamp mechanism being arranged on the same side of the support, the lamp mechanism operating to project a beam onto the load and the load acting to reflect the beam onto the photocell.

2. A lift truck including a load support and a hoist motor connected thereto for raising or lowering the same, control mechanism operatively connected to the hoist motor, a photocell operatively connected to said control mechanism and arranged to receive a beam of light reflected from a load on the load support, and lamp mechanism arranged and operating to project a beam of light toward a load on the support, said projected beam of light and said reflected beam being arranged at an acute angle to each other and the photocell and lamp mechanism being adjustable vertically and arranged on the same side of the support, the lamp mechanism operating to project a beam onto the load and the load acting to reflect the beam onto the photocell when the load reaches a predetermined level.

3. A lift truck including a load support and a hoist motor operatively connected thereto for raising or lowering the same, a control switch operatively connected to the motor, a photocell operatively associated with said control switch and arranged to receive a beam of light reflected from a load on the load support, and light mechanism operating to project a beam of light onto a load on the load support, said light beam being refiected by the load onto the photocell in a direction an acute angle to the direction of the beam of light when the load is in the path of the projected light beam.

4:. A lift truck including a load support and a hoist motor operatively connected thereto for raising or lowering the same, a control switch operatively connected to the motor and normally held in one position, a photoelectric relay governing the control switch and operable to move it to a second position, a photocell operatively con.- nected to said photoelectric relay and arranged to receive a beam of light reflected from a load on the load support, and light mechanism operating to project a beam of light onto a load on the load support, said beam being reflected by the load onto said photocell in a direction at an acute angle to the direction of said projected beam of light when the load is in the path of the projected beam.

5. A lift truck including a load support and a hoist motor operatively connected thereto for raising or lowering the same, a control switch operatively connected to the motor and normally held in one position, a photoelectric relay governing the control switch and operable to move it to a second position, a photocell operatively connected to said photoelectric relay and arranged to receive a beam of light reflected from a load on the load support, and light mechanism operating to project a beam of light onto a load on the load support, said light mechanism and photocell being located on the same side of the load support and adjustable vertically, said reflected beam being arranged at an acute angle to the projected beam and acting to reflect the beam onto the photocell.

5. A lift truck includin a load support, a hoist motor operatively connected thereto for raising or lowering the same, reversing means for operating the motor in either direction, and solenoids controlling said reversing means, a control switch governing said solenoids and normally held in one position, a photoelectric relay operatively connected to said control switch and operable to move it to a second position, a photocell operatively connected to said photoelectric relay and arranged to receive a beam of light reflected from a load on the load support, and light mechanism arranged and operating to project a beam of light toward the load, said beam being reflected onto the photocell in a direction at an acute angle to the direction of said projected beam of light when the load is in the path of the beam and. the photocell and light mechanism being vertically adjustable.

7. A lift truck including a load support, a hoist motor operatively connected thereto for raising or lowering the same, and reversing switch connected to said motor, solenoids operatively connected to said reversing switch, a photocell and light mechanism adjustable vertically on the truck, the light mechanism being arranged and operating to project a beam of light toward the load and the photocell arranged to receive the refiected beam of light when the load is in the path of said beam, said reflected beam being at an acute angle to said projected beam of light, a photoelectric relay governed by said photocell, and a control switch connected to said relay and governing said solenoids, said control switch being normally in one position and operated to a second position by said relay.

8. A lift truck including a load support, a hoist motor operatively connected thereto for raising or lowering the same, and a reversing switch connected to said motor and operable to move it in either direction, solenoids operatively connected to said reversing switch, a control switch movable to either of two positions and operable to actuate one or the other of said solenoids, a photoelectric relay operatively connected to said control switch and held normally in position to actuate the raising solenoid, a vertically adjustable photocell operatively connected to said photoelectric relay, and vertically adjustable light mechanism,

operating to project a beam of light onto a load on the load support, the load acting to reflect the beam of light onto the photocell, said reflected beam being at an acute angle to said projected beam of light and said photocell acting to control movement of the load support when the load is in the path of the beam.

9. A lift truck including a load support, a hoist motor operatively connected thereto for raising or lowering the same, and a reversing switch connected to said motor, solenoids connected to said reversing switch, a control switch movable to either of two positions and operating to actuate one or the other of said solenoids, a photoelectric relay operatively connected to said control switch and held normally in position to actuate the raising solenoid, a photocell operatively connected to said photoelectric relay, lamp mechanism operating to project a beam of light toward the load support whereby said beam is reflected onto said photocell when a load is in the path of the beam, said reflected beam being at an acute angle to said projected beam of light, an electric circuit connected to said hoist motor, lamp mechanism, photoelectric relay and solenoids, a selector automatic switch in said circuit movable to either raise or lower position operating to govern said control switch for raising or lowering the load support automatically, a selector hand switch in said circuit operable to raise or lower the load support by manual control, and a main switch in said circuit operable to permit control of said solenoids either automatically or manually.

10. A lift truck including a load support, a hoist motor operatively connected thereto for raising or lowering the same, and a reversing switch connected to said motor, solenoids connected to said reversing switch, a control switch movable to either of two positions and operating to actuate one or the other of said solenoids, a photoelectric relay operatively connected to said control switch and held normally in position to actuate the raising solenoid, a photocell operatively connected to said photoelectric relay, lamp mechanism operating to project a beam of light toward the load support whereby said beam is reflected onto said photocell when a load in the path of the beam, said reflected beam being at an acute angle to said projected beam of light, an electric circuit connected to said hoist motor, lamp mechanism, photoelectric relay and solenoids, a selector automatic switch in said circuit movable to either raise or lower position operating to govern said control switch for raising or lowering the load support automatically, a selector hand switch in said circuit operable to raise or lower the load support by manual control, and a main switch in said circuit operable to permit control of said solenoids either automatically or menually, said lamp mechanism and photocell being located on the same side of the load support and adjustable vertically.

11. A lift truck including a load support, a hoist motor operatively connected thereto for raising or lowering the same, and a reversing switch connected to said motor, raising and lowering solenoids connected to said reversing switch, a control switch movable to either of two positions and operating to actuate one or the other of said solenoids, a photoelectric relay operatively connected to said control switch and held normally in position to actuate the raising solenoid, said relay when actuated operating to move the control switch into position to operate the lowering solenoid, a selector automatic switch in the circuit with said control switch and movable to raise or lower position, said selector switch when in raise position breaking the circuit to the lowering solenoid and when in lower position breaking the circuit to the raising solenoid, a photocell operatively connected to said photoelectric relay, and light mechanism arranged to project a beam of light onto the load on the load support and said beam being reflected onto the photocell in a direction at an acute angle to the direction of said projected beam of light when the load is in the path of the beam of light.

12. A lift truck including a load support, a hoist motor operatively connected thereto for raising or lowering the same, and a reversing switch connected to said motor, raising and lowering solenoids connected to said reversing switch, a control switch movable to either of two positions and operating to actuate one or the other of said solenoids, a photoelectric relay operatively connected to said control switch and held normally in position to actuate the raising solenoid, said relay when actuated operating to move the control switch into position to operate the lowering solenoid. a selector automatic switch in the circuit with said control switch and movable to raise or lower position, said selector switch when in raise position breaking the circult to the lowering solenoid and when in vertically adjustable and located on the same side 7 lower position breaking the circuit to the raisof the load support.

ing solenoid, a photocell operatively connected ARTHUR S. HAMILTON, JR. to said photoelectric relay, and light mechanism arranged to project a beam of light onto the load 5 References clted m the file of thls patent on the load support and said beam being reflected UNITED STATES PATENTS onto the photocell when the load is in the path of the beam of light, said reflected beam being at gg gz a if an acute angle to said proJeoted beam of light 2,547,201 Fegely Arm 3 1951 and said photocell and lamp mechanism being 10 2 583 580 Ludwig Jan 29 1952 

